Electrical appliances such as image forming apparatuses generally include an operation input section on which a key input operation is performed for setting functions (see, for example, Japanese Unexamined Patent Publication No. 2004-181775).
In some case, a plurality of functions are assigned to one key and executed depending on the way of pressing the key. Unless pressing the key in a correct way, a user cannot perform a desired key input operation. For example, key input operations to be performed by pressing one key include: inputting a specific value (e.g., “1”) by pressing the key for 0.5 second; inputting a signal for cancellation of the input value (“1” in this case) by pressing the key twice in one second; and inputting another value (e.g., “10”) by continuously pressing the key for not shorter than one second. In this case, the user can input a desired value or cancel the input value only when the user correctly presses the key for the corresponding key pressing period preliminarily defined.
However, the key pressing period for performing the key input operation varies depending on the user, so that a predetermined allowance should be provided to the key pressing period for detection of the key input operation in the case of a shared image forming apparatus. However, a greater allowance of the key pressing period for the detection of the key input operation is not preferred, because a user's unintended input (disturbance) caused, for example, by inadvertently touching the key for a moment is mistakenly regarded as a key input operation.